r/nut{,-monitor}: Enable nut.target

Recent versions of NUT have a *nut.target* unit that collects all of the
NUT-related services.  Enabling any of the services individually does
effectively nothing, as it only adds the service as a `Wants` dependency
for *nut.target*, and that unit already has dependencies for all of
them. Thus, in order for the service to start at boot, *nut.target* has
to be enabled instead.

In situations where only *nut-monitor* should be enabled, enabling
*nut.target* is inappropriate, since that enables *nut-driver* and
*nut-server* as well. It's not clear why upstream made this change (it
was part of a [HUGE pull request][0]), but restoring the desired
behavior is easy enough by clearing the dependencies from *nut.target*.
Services that we want to start automatically can still be enabled
individually, and will start as long as *nut.target* is enabled.

[0]: https://github.com/networkupstools/nut/pull/330

roles/nut-common/files/nut-reset-deps.conf

@@ -0,0 +1,3 @@
+[Unit]
+Wants=
+Requires=

roles/nut-common/tasks/main.yml

@@ -0,0 +1,26 @@
+- name: ensure nut.target configuration drop-in directory exists
+  file:
+    path: /etc/systemd/system/nut.target.d
+    owner: root
+    group: root
+    mode: u=rwx,go=rx
+    state: directory
+  tags:
+  - systemd
+
+- name: ensure nut.target dependencies are reset
+  copy:
+    src: nut-reset-deps.conf
+    dest: /etc/systemd/system/nut.target.d/reset-deps.conf
+    owner: root
+    group: root
+    mode: u=rw,go=r
+  tags:
+  - systemd
+
+- name: ensure nut.target is enabled
+  systemd:
+    name: nut.target
+    enabled: true
+  tags:
+  - service

roles/nut-monitor/tasks/main.yml

@@ -33,3 +33,7 @@
     enabled: true
   tags:
   - service
+
+- name: apply nut-common role
+  include_role:
+    name: nut-common

roles/nut/tasks/main.yml

@@ -60,3 +60,7 @@
     permanent: true
   tags:
   - firewalld
+
+- name: apply nut-common role
+  include_role:
+    name: nut-common